When you block a contact/number on HTC 10 you'll no longer receive any call or message for that blocked person. To block/unblock a contact/number on HTC 10, do as follows:
1. Open the People app on your HTC 10 (Or open the Phone app and swipe to the people tab)
2. Hit the 3-dot icon followed by the Manage Contacts settings
3. Touch to open the Blocked Contacts settings
4. Hit the Add (+) button on the top right and select either Choose from Contacts or Add Number option
5. If selecting from contacts, mark the contact(s) you would like to Block and then hit the Save button
To unblock a contact/number on HTC 10, do as follows:
1. On the Blocked Contacts menu, press and hold your finger on the contact you want to unblock
2. And simply touch the Unblock Contacts option
3. Press OK to confirm